Ammonium Bromide (ammonium + bromide)

Distribution by Scientific Domains

Kinds of Ammonium Bromide

  • cetyl trimethyl ammonium bromide
  • trimethyl ammonium bromide


  • Selected Abstracts


    ChemInform Abstract: Guanidinium Nitrate/Silica Sulfuric Acid/Ammonium Bromide as an Effective, Viable and Metal-Free Catalytic Media for the Selective Oxidation of Sulfides to the Sulfoxides.

    CHEMINFORM, Issue 19 2010
    Mohsen Nikoorazm
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Mild and Regioselective Oxidative Bromination of Aromatic Compounds Using Ammonium Bromide and Oxone.

    CHEMINFORM, Issue 15 2004
    N. Narender
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    Synthesis and properties of ,-Fe2O3 nanorods

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2010
    R. Ramesh
    Abstract We report synthesis of ,-Fe2O3 (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 C. The calcined ,-Fe2O3 nanorods were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the ,-Fe2O3 nanorods were hexagonal structure. The nanorods have diameter of 30-50 nm and length of 120-150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Synthesis and comparative physicochemical investigation of partly aromatic cardo copolyesters

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007
    N. B. Joshi
    Abstract Copolyesters were synthesized through the condensation of 0.0025 mol of 1,1,-bis(3-methyl-4-hydroxyphenyl)cyclohexane, 0.0025 mol of ethylene glycol/propylene glycol/1,4-butanediol/1,6-hexane diol, and 0.005 mol of terephthaloyl chloride with water/chloroform (4:1 v/v) as an interphase, 0.0125 mol of sodium hydroxide as an acid acceptor, and 50 mg of cetyl trimethyl ammonium bromide as an emulsifier. The reaction time and temperature were 2 h and 0C, respectively. The yields of the copolyesters were 81,96%. The structures of the copolyesters were supported by Fourier transform infrared and 1H-NMR spectral data and were characterized with the solution viscosity and density by a floatation method (1.1011,1.2697 g/cm3). Both the intrinsic viscosity and density of the copolyesters decreased with the nature and alkyl chain length of the diol. The copolyesters possessed fairly good hydrolytic stability against water and 10% solutions of acids, alkalis, and salts at room temperature. The copolyesters possessed moderate-to-good tensile strength (11,37.5 MPa), good-to-excellent electric strength (19,45.6 kV/mm), excellent volume resistivity (3.8 1015 to 2.56 1017 , cm), and high glass-transition temperatures (148,195C) and were thermally stable up to about 408,427C in a nitrogen atmosphere; they followed single-step degradation kinetics involving 38,58% weight losses and 34,59% residues. The copolyesters followed 2.6,2.9-order degradation kinetics. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]


    Synthesis and characterization of novel poly(o -toluidine) montmorillonite nanocomposites: Effect of surfactant on intercalation

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007
    Rahul Singhal
    Abstract The investigation of clay based polymer nanocomposites has opened the door for the development of novel, ecofriendly advanced nano materials that can be safely recycled. Because of their nanometer size dispersion, these nanocomposites often have superior physical and mechanical properties. In this study, novel nanocomposites of poly(o -toluidine) (POT) and organically modified montmorillonite (MMT) were synthesized using camphor sulfonic acid (CSA), cetyl pyridinum chloride (CPCl), and N -cetyl- N,N,N -trimethyl ammonium bromide (CTAB) to study the role of surfactant modification on the intercalation. The in situ intercalative polymerization of POT within the organically modified MMT layers was analyzed by FTIR, UV,visible, XRD, SEM as well as TEM studies. The average particle size of the nanocomposites was found to be in the range 80,100 nm. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source]


    The use of colloidal gas aphrons as novel downstream processing for the recovery of astaxanthin from cells of Phaffia rhodozyma

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2008
    Maria Dermiki
    Abstract BACKGROUND: There is an increasing interest in obtaining natural products with bioactive properties, using fermentation technology. However, the downstream processing consisting of multiple steps can be complicated, leading to increase in the final cost of the product. Therefore there is a need for integrated, cost-effective and scalable separation processes. RESULTS: The present study investigates the use of colloidal gas aphrons (CGA), which are surfactant-stabilized microbubbles, as a novel method for downstream processing. More particularly, their application for the recovery of astaxanthin from the cells of Phaffia rhodozyma is explored. Research carried out with standard solutions of astaxanthin and CGA generated from the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) showed that up to 90% recovery can be achieved under optimum conditions, i.e., pH 11 with NaOH 0.2 mol L,1. In the case of the cells' suspension from the fermentation broth, three different approaches were investigated: (a) the conventional integrated approach where CGA were applied directly; (b) CGA were applied to the clarified suspension of cells; and finally (c) the in situ approach, where CGA are generated within the clarified suspension of cells. Interestingly, in the case of the whole suspension (approach a) highest recoveries (78%) were achieved under the same conditions found to be optimal for the standard solutions. In addition, up to 97% recovery of total carotenoids could be achieved from the clarified suspension after pretreatment with NaOH. This pretreatment led to maximum cell disruption as well as optimum conditioning for subsequent CGA separation. CONCLUSIONS: These results demonstrate the potential of CGA for the recovery of bioactive components from complex feedstock. Copyright 2008 Society of Chemical Industry [source]


    Kinetic study on the prooxidative effect of vitamin C on the autoxidation of glycerol trioleate in micelles

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2006
    Zai-Qun Liu
    Abstract Vitamin C (L -ascorbic acid) protects human health by scavenging toxic free radicals and other reactive oxygen species formed in cell metabolism. The surplus supplementation of vitamin C, however, may be harmful to health because the level of 8-oxoguanine and 8-oxoadenine in lymphocyte DNA varies remarkably. In the process of the kinetic investigation on the 2,2,-azobis(2-amidinopropane dihydrochloride) (AAPH)-induced autoxidation of glycerol trioleate (GtH) in the micelles of cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X-100, the addition of vitamin C accelerates the autoxidation of GtH even in the absence of the free radical initiator, AAPH. The initiating rate, Ri, of vitamin C (VC)-induced autoxidation of GtH is related to the micelle charge, i.e. Ri,=,14.4,,10,6 [VC] s,1 in SDS (anionic micelle), Ri,=,1961,,10,6 [VC] s,1 in Triton X-100 (neutral micelle) and Ri is a maximum in CTAB (cationic micelle) when the vitamin C concentration is ,300,M. Thus, vitamin C can initiate autoxidation of GtH in micelles, especially in the neutral one. Moreover, the attempt to explore whether ,-tocopherol (TocH) could rectify vitamin C-induced autoxidation of GtH leads us to find that the rate constant of TocH reacting with the anionic radical of vitamin C (VC.,), k,inh, is ,103M,1,s,1, which is less than that of the ,-tocopherol radical (Toc.) with vitamin C (kinh,=,,105,M,1,s,1). Thus, the equilibrium constant of the reaction Toc.+VC,,TocH+VC., is prone strongly to the regeneration of Toc. by vitamin C rather than the reverse reaction. Copyright 2006 John Wiley & Sons, Ltd. [source]


    Micelle-to-vesicle transition induced by oligonucleotide in SDS/DEAB mixed system with a net negative charge

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2008
    Xia Guo
    Abstract Sodium dodecyl sulfate (SDS)/dodecyl triethyl ammonium bromide (DEAB) mixed micelles (with SDS in excess) can transform to vesicles only when the temperature is higher than a critical value. In this study, we report for the first time that oligonucleotide can decrease the critical temperature to a much lower value and, hence, induce micelle-to-vesicle transition. The facilitation efficiency of oligonucleotide on vesicle formation is closely dependent on its size and base composition. Moreover, the SDS/DEAB/oligonucleotide vesicles are negatively charged and the hydrophobic interaction between oligonucleotide and SDS/DEAB mixed micelles is the driving force. As, so far, the report about the facilitation effect of oligonucleotide and DNA on vesicle formation is very limited, this study may provide some helpful information for the application of DNA/amphiphile system. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7491,7504, 2008 [source]


    Self-initiation of the UV photopolymerization of brominated acrylates

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008
    Tom Scherzer
    Abstract Brominated aromatic acrylates were found to polymerize rapidly upon exposure to UV light. Moreover, they are able to initiate the UV-induced polymerization of acrylic formulations that do not contain a conventional photoinitiator. In contrast, the corresponding unbrominated homologues are not effective as initiators. Investigations by real-time FTIR spectroscopy have shown that the addition of only 1 wt % of a brominated acrylate is sufficient for an efficient initiation. Fast photopolymerization is achieved even if irradiation is carried out at , > 300 nm where most acrylates do not absorb. Short-lived transients were studied by laser flash photolysis. The triplet was found to show low sensitivity to oxygen which is because of its very short lifetime. Bromine radicals split of from the acrylates were trapped with bromine ions from tetraethyl ammonium bromide and detected as Br. The resulting quantum yields for the formation of bromine radicals are in the range of up to 0.3. Quantum chemical modeling was carried out to establish a mechanism for the release of bromine radicals. Both bromine and bromophenyl radicals are able to initiate the polymerization reaction. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4905,4916, 2008 [source]


    Nonaqueous dispersion polymerization of styrene in methanol with the ionomer block copolymer poly[(4-methylstyrene)- co -(4-vinyltriethylbenzyl ammonium bromide)]- b -polyisobutene as a stabilizer

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2004
    Yuhong Ma
    Abstract The nonaqueous dispersion polymerization of styrene in methanol with poly[(4-methylstyrene)- co -(4-vinyltriethylbenzyl ammonium bromide)]- b -polyisobutene as a stabilizer was investigated. There was no observable inducing period or autoacceleration in the polymerization process. The conversion increased almost linearly with the polymerization time as high as 80%. The average sizes of the obtained polystyrene particles increased, and the size distributions of the polystyrene particles tended to become narrower, with increasing conversion. The mechanism of the dispersion polymerization in the presence of polyisobutene- b -poly[(4-methylstyrene)- co -(4-vinyltriethylbenzyl ammonium bromide)] was nucleation/growth. When the stabilizer/monomer ratio (w/w) was greater than 2.0%, the polystyrene dispersion was stable, and there was no observable polymer particle coagulation taking place during the whole polymerization process. The average diameter of the polymer particles can be mediated through changes in the polymerization conversion, monomer, and stabilizer. Nearly monodispersed polystyrene particles with average diameters of approximately 0.45,2.21 ,m were obtained under optimal conditions. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2678,2685, 2004 [source]


    In vitro and in vivo antifungal activity of cetrimide (cetyltrimethyl ammonium bromide) against fungal keratitis caused by Fusarium solani

    MYCOSES, Issue 1 2007
    Yehia A.-G.
    Summary Mycotic keratitis is a devastating eye infection acquired after eye injury. Cetrimide at 15 and 20 mg ml,1 produced no surviving Fusarium solani growth with minimal inhibitory concentration value of 0.10 mg ml,1. Topical administration of three drops (0.3 ml) of cetrimide aqueous solution of 10 mg ml,1 at pH 6.4 three times daily succeeded to cure human severe resistant F. solani keratitis in a time course of <3 weeks, and with complete healing after 6 weeks. Cetrimide-treated rabbit corneas section appeared with normal compact epithelium and endothelium with no vacuolation in Descemet's endothelial complex: an indication that cetrimide has no significant toxic effects. So, cetrimide at 10 mg ml,1 may be effective and safe topical therapy in patients with mycotic keratitis, especially F. solani ulcers. Currently, there is no antimycotic drug with a good corneal penetration, which is safe and has a fungicidal activity. [source]


    Kinetics of the M-Intermediate in the Photocycle of Bacteriorhodopsin upon Chemical Modification with Surfactants

    PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2010
    Li-Kang Chu
    The spectroscopic and kinetic studies of the interaction between bacteriorhodopsin in the M-intermediate and several surfactants (cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, diethylene glycol mono- n -hexyl ether, ethylene glycol mono- n -hexyl ether, sodium 1-decanesulfonate and sodium 1-heptanesulfonate) have been investigated using steady-state UV,VIS spectrometry and time-resolved absorption techniques. The steady-state spectral results show that bR retains its trimeric state. Time-resolved observations indicate that the rate of deprotonation of the protonated Schiff base increases in the presence of the cationic surfactants, whereas insignificant changes are observed in the neutral or anionic surfactants. The rate of the reprotonation of the Schiff base in the transition M , N is accelerated in anionic and neutral surfactants, but is decelerated in the presence of the cationic surfactants. Surfactants with a longer hydrocarbon tail have a greater effect on the kinetics when compared with surfactants having shorter hydrocarbon tails. The opposite effect is observed when the hydrophilic head of the surfactants contains opposite charges. These distinct kinetics are discussed in terms of the difference in the modified surface hydrophilicity of the bR and the possible protein configurational changes upon surfactant treatments. [source]


    A comparative study of transformation of micellar structures in CTAB and TTAB binary systems using Positron Lifetime Spectroscopy

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
    R. Yadav
    Abstract The micellar structures of cetyl-tri-methyl ammonium bromide (CTAB) and its homologues have been investigated employing several conventional techniques. However, due to lack of sensitivity inherent in these techniques and the perturbation introduced by the probe, the detailed structures of the aggregates in the so-called single phase regions of these systems are far from being fully understood. Positron has been found to be a useful non-destructive probe for investigating micellar structures in surfactant systems [1-3] The present study is an effort to get a better insight into the micellar structures and their transformations in CTAB and TTAB aqueous binary systems Positron lifetime spectroscopy has been employed to study these systems covering a wide range of surfactant concentrations. A comparative study of the results obtained for the two surfactant systems have been discussed in this paper. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    The preparation of MnZn-ferrite nanoparticles in a water/CTAB, 1-butanol/1-hexanol reverse microemulsion

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004

    Abstract Manganese zinc ferrite nanoparticles were prepared using a precipitation in reverse microemulsion system consisting of hexadecyltrimethyl ammonium bromide (CTAB) as a surfactant, 1-butanol as a co-surfactant, 1-hexanol as an oil phase and an aqueous solution of metal sulfates. Tetramethyl ammonium hydroxide (TMAH) served as the precipitating agent. The influence of the microemulsion's composition on the nature of the spinel product was studied. The synthesized nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffractometry (XRD), specific surface area (BET) and magnetometry. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Use of different alkylammonium salts in clay surface modification for epoxy-based nanocomposites

    POLYMER COMPOSITES, Issue 3 2009
    G. Ipek Nakas
    Layered silicates become widely used reinforcement material in the polymer nanocomposite production in recent years due to their high aspect ratio, ease of processing, and low cost. In this present study, the aim was to evaluate the usability of a raw clay source (Resadiye, Turkey) in the production of epoxy/clay nanocomposites and to investigate the effects of different surface modifiers. For this purpose, raw Na,montmorillonite clay was first purified and then surface modified by using different types of alkylammonium salts: tetramethyl ammonium bromide, benzyl triethyl ammonium bromide, dodecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, and octadecyl trimethyl ammonium bromide. Purification and surface modification of this clay were evaluated by using the following analyses; X-ray diffraction (XRD), cation exchange capacity (CEC), particle size distribution, and dissolved organic content. These analyses simply indicated that surface modification increased both interlayer spacing between the silicate layers and CEC of the clay. These improvements were directly proportional with the chain length of the surface modifier. Nanocomposite specimens were produced by adding 0.5 wt% surface modified clay into the epoxy matrix. These specimens were characterized by XRD, Si-mapping facility of SEM, and mechanical tests. XRD results indicated an exfoliated structure whereas Si-mapping showed the uniform distribution of clay particles in epoxy, leading to improved mechanical properties, for instance more than 100% increase in fracture toughness of the neat epoxy specimen. POLYM. COMPOS., 2009. 2008 Society of Plastics Engineers [source]


    Preparation and properties of polyurethane/montmorillonite nanocomposites cured under room temperature

    POLYMER COMPOSITES, Issue 5 2006
    Hangbin Jiang
    The polyurethane/C16C18 -MMT (the montmorillonite modified with cetyloctadecyldimethyl ammonium bromide) nanocomposites were synthesized by intercalative polymerization and cured under room temperature. The d -spacing and the dispersion of the C16C18 -MMT in the nanocomposites were measured by X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM). The mechanical and thermal properties of the nanocomposites were measured by Universal Testing System, Electric Anti-fold Instrument, Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC). It was found out that introducing C16C18 -montmorillonite (MMT) in the polyurethane (PU) displayed good mechanical properties and thermal stability. Rheology behavior in liquid state showed that the addition of the C16C18 -MMT to PU resulted in low gel time and high viscosity. POLYM. COMPOS. 27:470,474, 2006. 2006 Society of Plastics Engineers. [source]


    Effect of clay/water ratio during bentonite clay organophilization on the characteristics of the organobentonites and its polypropylene nanocomposites

    POLYMER ENGINEERING & SCIENCE, Issue 9 2009
    Sudina M.L. Silva
    A sodium bentonite (montmorillonite-based layered silicate clay) was organically modified with cetyl trimethyl ammonium bromide (cetrimide), using different clay/water ratios,but the same clay/cetrimide ratio,to suspend the bentonite clay and perform its organophilization. Infrared spectroscopy and thermogravimetric analysis indicated the incorporation of organic modifier into the bentonite. Wide-angle X-ray scattering showed that the incorporation of surfactant significantly increased the interlayer spacing in the bentonite for all concentrations studied. It was found that clay/water ratio employed during the modification affects neither the amount of organic salt incorporated nor the interlayer spacing in the organobentonites, but influences its degree of structural disorder. Lower clay/water ratios resulted in a more disorderly structure, as established by the decrease of the areas under the X-ray peaks as the clay/water ratio diminishes. The modified bentonites were melt compounded with maleic anhydride-grafted polypropylene. X-ray diffraction patterns of the hybrids revealed that the more disorderly organobentonites were better dispersed in the polymer matrix, indicating that, in the present system, the structure of polymer nanocomposites obtained were affected by the clay/water ratio used in organobentonite preparation. POLYM. ENG. SCI., 2009. 2009 Society of Plastics Engineers [source]


    Epoxy nanocomposites curing by microwaves

    POLYMER ENGINEERING & SCIENCE, Issue 8 2006
    Nurseli Uyan
    In this work, chemically modified sodium montmorillonite and epoxy monomer were used to prepare nanocomposites in two consecutive stages. In the first stage, dodecylamine, octadecylamine, hexadecylamine, and hexadecyltrimethyl ammonium bromide were used to prepare various organophilic clays. In the second stage, the bisphenol-A based epoxy monomer and predetermined amounts of organoclay were mixed together and then cured by an aliphatic polyamine for 20 min under microwave at 400 W. Furthermore, ,-, diacrylate poly(dimethylsiloxane) was added to the mixture before the curing process to modify the toughness of the samples. The mixture was poured into the poly(tetrafluoroethylene) mold; the epoxy resin/curing agent ratio was maintained as 2/1. The clear films formed after microwave irradiation were removed from the mold, cooled, and then stored in a cool and dry medium until characterization. The samples were analyzed by wide angle X-ray diffraction, differential scanning calorimetry, and mechanical tests. Surfaces of the cold fractured samples were also observed under the scanning electron microscope. The results revealed that microwave curing of the samples of 5% organoclay and 5% siloxane showed improvement in mechanical properties. POLYM. ENG. SCI. 46:1104,1110, 2006. 2006 Society of Plastics Engineers [source]


    Removal of dyes from water by poly(vinyl pyrrolidone) hydrogel,

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2006
    Bahire Filiz Senkal
    Abstract The interaction between polymer and dye leading to polymer-dye complex formation exhibits many interesting and important practical features. For this purpose, a hydrogel was prepared by crosslinking copolymerization of vinyl pyrrolidone with tetraallyl ammonium bromide in aqueous solution, using K2S2O8 as a radical initiator. Dye extraction experiments were carried out simply by contacting wetted gel samples with aqueous dye solutions at room temperature. Capacities were determined by colorimetric analysis of the residual dye contents. The hydrogel swelled in water showing that reasonable high dye sorption capacity (0.71,1.13,g per gram of gel) was achieved. This material is also able to remove the anionic dyes completely even from highly diluted aqueous dye solutions. No trace absorbance was detected in the visible range, after processing. Copyright 2006 John Wiley & Sons, Ltd. [source]


    Separation of astaxanthin from cells of Phaffia rhodozyma using colloidal gas aphrons in a flotation column

    BIOTECHNOLOGY PROGRESS, Issue 2 2010
    Maria Dermiki
    Abstract The aim of this study is to investigate the separation of astaxanthin from the cells of Phaffia rhodozyma using colloidal gas aphrons (CGA), which are surfactant stabilized microbubbles, in a flotation column. It was reported in previous studies that optimum recoveries are achieved at conditions that favor electrostatic interactions. Therefore, in this study, CGA generated from the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) were applied to suspensions of cells pretreated with NaOH. The different operation modes (batch or continuous) and the effect of volumetric ratio of CGA to feed, initial concentration of feed, operating height, and flow rate of CGA on the separation of astaxanthin were investigated. The volumetric ratio was found to have a significant effect on the separation of astaxanthin for both batch and continuous experiments. Additionally, the effect of homogenization of the cells on the purity of the recovered fractions was investigated, showing that the homogenization resulted in increased purity. Moreover, different concentrations of surfactant were used for the generation of CGA for the recovery of astaxanthin on batch mode; it was found that recoveries up to 98% could be achieved using CGA generated from a CTAB solution 0.8 mM, which is below the CTAB critical micellar concentration (CMC). These results offer important information for the scale-up of the separation of astaxanthin from the cells of P. rhodozyma using CGA. 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source]


    Role of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte Complexes

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007
    Yuxia Luan Dr.
    Abstract Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed. [source]


    Solubilization of Single-Walled Carbon Nanotubes by using Polycyclic Aromatic Ammonium Amphiphiles in Water,Strategy for the Design of High-Performance Solubilizers

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2006
    Yasuhiko Tomonari
    Abstract We describe the design of polycyclic aromatic compounds with high performance that dissolve single-walled carbon nanotubes (SWNTs). Synthetic amphiphiles trimethyl-(2-oxo-2-phenylethyl)-ammonium bromide (1) and trimethyl-(2-naphthalen-2-yl-2-oxo-ethyl)-ammonium bromide (2) carrying a phenyl or a naphtyl moiety were not able to dissolve/disperse SWNTs in water. By contrast, trimethyl-(2-oxo-2-phenanthren-9-yl-ethyl)-ammonium bromide (3) solubilized SWNTs, although the solubilization ability was lower than that of trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (4) (solubilization behavior observed by using 4 was described briefly in reference 4a). Transmission electron microscopy (TEM), as well as visible/near-IR, fluorescence, and near-IR photoluminescence spectroscopies were employed to reveal the solubilization properties of 4 in water, and to compare these results with those obtained by using sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB) as solubilizers. Compound 4 solubilized both the as-produced SWNTs (raw-SWNTs) and purified SWNTs under mild experimental conditions, and the solubilization ability was better than that of SDS and HTAB. Near-IR photoluminescence measurements revealed that the chiral indices of the SWNTs dissolved in an aqueous solution of 4 were quite different from those obtained by using micelles of SDS and HTAB; for a SWNTs/4 solution, the intensity of the (7,6), (9,5), and (12,1) indices were strong and the chirality distribution was narrower than those of the micellar solutions. This indicates that the aqueous solution of 4 has a tendency to dissolve semiconducting SWNTs with diameters in the range of 0.89,1.0 nm, which are larger than those SWNTs (0.76,0.97 nm) dissolved in the aqueous micelles of SDS and HTAB. [source]


    Preparation of Mesoporous Molecular Sieves Al-MSU-S Using Ionic Liquids as Template

    CHINESE JOURNAL OF CHEMISTRY, Issue 10 2006
    Xin-Yu Yu
    Abstract Mesoporous molecular sieves Al-MSU-S has been prepared from the precursor of zeolite Y using ionic liquids 1-hexadecane-3-methylimidazolium bromide (CMIMB) as a template in basic medium, which exhibited larger pore diameter, pore volume and surface area than that synthesized using cetyl trimethyl ammonium bromide (CTAB) template. [source]


    Effect of Sodium Halide on Dynamic Surface Tension of a Cationic Surfactant

    CHINESE JOURNAL OF CHEMISTRY, Issue 8 2005
    L Feng-Feng
    Abstract The equilibrium and dynamic surface tension (DST) of the novel cationic surfactant, 3-(p -nonylphenoxy)-2-hydroxylpropyl trimethyl ammonium bromide, abbreviated as RTAB, were studied. The effect of sodium halide such as NaCl, NaBr and NaI on the DST behavior of the RTAB solution below its CMC was studied in detail. Due to the preferential adsorption, the effect of hydration and salting out, the ability to reduce the DST values at the same concentration was in the order of NaI>NaBr>NaCl. Attributed to its high surface activity, the equilibrium time of the DST of the surfactant solution was insensitive to the ionic strength. [source]


    Phase-Transfer-Catalyzed Enantioselective Mannich Reaction of Malonates with ,-Amido Sulfones

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 15 2006
    Francesco Fini
    Abstract The highly enantioselective reaction between in situ generated, Cbz-protected azomethines and malonates in the presence of 150 mol,% of potassium carbonate (50,% w/w) and 1 mol,% of quinine-derived quaternary ammonium bromides as phase-transfer organocatalysts has been developed. This study reports a novel approach for the asymmetric Mannich-type reaction and a wide range of azomethines, including those derived from enolizable aldehydes, is tolerated by the present system. The adducts, obtained in excellent yields with ee up to 98,%, are suitable precursors of optically pure ,-amino acids. [source]